New Zealand Journal of Crop and Horticultural Science abstracts
Didymella exitialis on wheat in New Zealand
M. G. CROMEY1
S. GANEV2
M. BRAITHWAITE2
H. J. BODDINGTON1
1New Zealand Institute for Crop & Food
Research Limited
Private Bag 4704
Christchurch, New Zealand
2Plant Protection Centre
MAF Quality Management
P. O. Box 24
Lincoln, New Zealand
Abstract Didymella exitialis (Morini) Muller was
identified on wheat (Triticum aestivum L.) leaves collected during a
survey of New Zealand wheat crops in the 1990/91 season. This fungus was
identified on nine cultivars in the major wheat-growing areas and was present
in 19 out of 42 crops surveyed. In the 1992/93 season, D. exitialis
pseudothecia first occurred in late November and became increasingly common as
leaves and crops senesced. The teleomorph was more common than the
Ascochyta anamorph. Pseudothecia of D. exitialis were frequently
associated with leaf scorch symptoms, but were also often abundant over the
surface of senesced leaves. The elongate lesions were tan to dark brown in the
centre with diffuse margins. Thirty-two single ascospore isolates were made.
Cultures sporulated sparsely on potato dextrose agar under near-UV light,
producing the Ascochyta anamorph. Inoculation of wheat plants using
pycnidiospores from culture resulted in disease symptoms, mostly on the margins
and tips of leaves, after c. 2 weeks. Pseudothecia developed c. 2 weeks
later and D. exitialis was re-isolated from infected leaves. Large
differences in the leaf area covered with D. exitialis were found
between cultivars in three field trials. `Otane' and `Norseman' were severely
affected in all trials, whereas `Monad' and `Kokako' were almost unaffected.
Didymella exitialis has not previously been recorded on wheat in New
Zealand.
Keywords wheat; leaf scorch; Didymella exitialis;
incidence; resistance
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